Consider adding the Debian Fast Track APT repo
Debian Fast Track is an alternative to Debian Backports where backports do not need to be done from Debian testing.
For instance, at the moment virtualbox-guest-*
are not installable from Sid into Buster (or Bullseye) any more due to too old libc6
(see #18643 (closed) for details) but Debian Fast Track offers packages for Buster (and Bullseye).
However, Debian Fast Track is not an official Debian project so we have to investigate what trusting them entails.
Edited by intrigeri